1. Field of the Invention
The present invention relates in general to an actuator which is widely used in hydraulic power transmission, such as for a transfer machine, an automatic stock feed, an automatic stamp, etc., and, in particular, to a new and useful actuator of which a piston rod can reciprocate in opposite axial directions and rotate in opposite angular directions.
2. Description of the Prior Art
There are known piston-cylinder actuators operable by the pressure of hydraulic fluid, but these actuators have cylinders of circular cross section. Accordingly, a piston rod of such circular cylinder can accurately effect reciprocable longitudinal movements but, when rotary movements of the piston rod are required in combination with longitudinal movements thereof, or when such actuator is used with a machine wherein a torque is effective on the piston rod, the piston rod cannot accurately effect longitudinal or rotary movements inasmuch as there is nothing to oppose rotation of the piston rod responsive to torques, exerted thereon, so that the piston rod might be rotated, responsive to applied torques, between longitudinal reciprocating movements. Consequently, in prior actuators, a projection which acts the part of a guide by being engaged with a groove which is provided on the piston is provided on the inside of the cylinder, whereby the piston rod permits accurate longitudinal or rotary movements in the event of the above-mentioned circumstances.
But, in such means, the durability of the actuator is reduced because it is unavoidable that the projection and groove are damaged by torques effective on the piston rod.